(1) Field of the Invention
The present invention relates to a yogurt product with increased shelf life containing a bacteriocin derived from a Pediococcus acidilactici. A preferred method for producing the yogurt product is by fermenting a milk based medium with Pediococcus acidilactici (PA), heating the medium to terminate growth of the Pediococcus acidilactici and fermenting the first fermentate after the heating with a yogurt culture to produce the yogurt product which contains bacteriocin active against undesirable flora.
(2) Prior Art
Yogurt products are well known and are produced by equal parts by cell count of Lactobacillus bulgaricus and Streptococcus thermophilus and are described, for instance, in U.S. Pat. Nos. 3,420,742 to Farr and 4,339,464 to Vedamuthu.
There are numerous foods which use yogurt as an ingredient in fluid or dried form. Some examples are salad dressings, sauces, baking mixtures, and other food systems requiring a tart, clean, lactic acid flavoring. There are a few dried yogurt powders available in the marketplace.
All the fluid and dried yogurt products currently available are made out of dairy bases which have either been acidified by direct addition of edible acids (primarily lactic acid and .delta.-gluconolactone for coagulation and acidity) or fermented using a yogurt starter bacteria. The fermented products in addition to dairy ingredients, contain dead, injured and live cells of yogurt bacteria and their metabolic by-products. Those products made by direct acidification will contain the acid(s) used for acidification. Dried yogurt powders can contain any neutralizing agent used to adjust the pH to the desirable range for good or acceptable dehydration of the product.
The usefulness of fluid and rehydrated yogurt products is in providing the specific textural and flavor attributes desired in the food system. Their addition to food systems is not intended to provide a barrier against spoilage or pathogenic bacteria which may gain entry into the food system. Acidity, if present, can provide very limited bacterial inhibition; however, neutralization limits this inhibition. It would be highly desirable to provide bacterial inhibition in the yogurt product.
Pediococcus acidilactici is known to produce a bacteriocin which has a broad spectrum against spoilage bacteria. Such bacteriocins are described in U.S. Pat. No. 4,929,445 to Vandenbergh et al; U.S. Pat. No. 5,175,252; U.S. Pat. No. 5,260,212, and U.S. Pat. No. 4,883,673 to Gonzalez et al.
Broad spectrum bacteriocins tend to retard the growth of yogurt cultures. This is true of nisin. Thus nisin has to be blended into the final product, thereby producing a significant risk of contamination of the final product.
It would be desirable if the bacteriocin could be introduced into the milk based medium used to produce the yogurt product. In this manner, the bacteriocin could protect the product as it was produced. The problem is that any acids or the like in excess generated by the bacteriocin producing cultures can inhibit the yogurt cultures.
Pediococcus acidilactici is used in meat fermentations. Generally it is not used commercially for milk fermentations because it grows poorly on milk based media. A Pediococcus which grows well in a milk based medium is needed.